1. Field of the Invention
The present invention relates to systems for controlling the workplace environment and, more particularly, relates to improved methods and apparatus for reducing the level of airborne particulate while increasing the comfort level of the working environment maintained at a pressure of slightly less than atmospheric pressure during operations involving the removal of hazardous material, such as asbestos or lead-based paint.
2. Description of the Background
Various systems have been devised to reduce workers' exposure to contaminants in the air while conducting operations which inevitably generate airborne particles. When such operations are part of a manufacturing process, permanent air ventilation, filtration, and exhaust systems are typically provided for efficiently reducing the airborne contaminant exposure to workers or operators. Special problems are presented, however, when high airborne contaminant levels occur in a workplace environment for relatively short periods of time, e.g., for only several days or weeks. As a practical matter, systems designed to reduce worker exposure at such work sites are typically portable, and are designed with little if any consideration to factors commonly considered when designing permanent air filtration installations. In many cases, workers exposed to hazardous airborne contaminants at differing work sites are provided with portable respirators which achieve adequate filtration of particles from the air inhaled by the worker, although the portable respirator may be cumbersome and impede the worker's performance.
A particularly troublesome problem is presented for workers performing operations including the removal or encapsulation of hazardous airborne contaminates, such as asbestos, from existing buildings. Asbestos fibers have long been known to cause significant health risks if inhaled, and accordingly protective equipment must be highly effective. Building asbestos abatement operations obviously are performed at different sites, and the building designs, asbestos containing materials, and the location of asbestos within the buildings widely vary. In spite of these difficulties, billions of dollars are spent annually and will continue to be expended to remove asbestos and similar contaminates from schools, offices, manufacturing plants, etc. in order to reduce the risks to personnel who daily occupy such buildings. Asbestos removal operations necessarily increase significantly the level of airborne asbestos fibers during the removal and cleanup procedure, and a significant amount of research and development has already been expended to devise systems to safeguard asbestos abatement workers. While such systems include protective suits, ventilators with portable air tanks, and other individualized equipment worn or carried by the workers, such safety equipment substantially reduces the dexterity and productivity of the worker and increases overall costs. Less cumbersome individualized safety equipment requires that airborne contamination levels at the workplace be substantially reduced so that any exposure to the workers will satisfy established guidelines. Moreover, such individualized equipment fails to satisfy the desire that hazardous airborne contaminants not leak from the work site.
U.S. Pat. No. 4,604,111 discloses a system for maintaining negative (less than atmospheric) pressure in an enclosure during asbestos removal operations by exhausting filtered air outside the substantially sealed workplace environment. This negative air system offers the advantage of reducing the likelihood that harmful fibers will escape the substantially sealed enclosure, since any leakage of air is inward toward the lower pressure within the workspace. Accordingly to the '111 patent, a flow path is established to allow outside air to intentionally leak into the substantially enclosed workspace, and this flow path is sealed by a flap seal of plastic sheeting to prevent air from exiting the enclosed space in the event of a loss of negative pressures.
Other systems have been devised which do not use the flap seal design described above. A HEPA-VENT system offered by Global Consumer Services utilizes self-closing solid doors to obtain worker access to an enclosed work area. The system filters makeup air which enters the enclosure, and also filters air from the enclosure if positive pressure were to build up within the enclosed workspace.
U.S. Pat. No. 4,801,312 discloses a system which establishes uniform airflow through the enclosed workspace to remove airborne particles from the worker's breathing zone. Air from the enclosed workspace is filtered by units positioned midway within the enclosed space, and the flow path between the inlet and outlet of these units remains within the enclosed space.
In spite of the advances made to date, significant problems remain for workers performing asbestos removal and cleanup operations within substantially enclosed workspaces. In most cases, a building in which asbestos abatement operations are conducted has a permanent heating, cooling, and ventilation system. This system cannot be operated during asbestos abatement operations, or the partially operated system must be completely isolated from the workspace where such asbestos abatement operations are occurring. The justified concern is that hazardous airborne particles may enter and contaminate the permanent building ventilation system, which could re-expose cleaned areas to contaminants and subject personnel without protective equipment to asbestos fibers for long periods of time.
Standard practice in the asbestos abatement industry is to define a contaminated working zone and avoid any system which exhausts contaminated air and circulates previously contaminated air back into the working zone. Permanent ventilation and air-conditioning systems typically use at least some outside air makeup, and their use during abatement operations would also defeat the objective of sealing off the enclosed area and maintaining a negative pressure within the enclosed space. A number of filtration and exhaust units are typically used to maintain negative pressure within the enclosed workspace, and the benefit of these units would be reduced by a system which added outside air to the enclosed space and thus tended to create a positive pressure within the defined working space.
Asbestos abatement personnel have long performed removal and cleanup operations under adverse temperature and humidity conditions. For example, personnel frequently are conducting operations in enclosed spaces where the temperature either exceeds 100.degree. F. or is less than 50.degree. F. Adverse environmental conditions substantially reduce the operator's productivity, especially when one considers the added burden on the operator attributable to protective clothing and required respiratory equipment. Moreover, asbestos abatement operations frequently involve water spraying techniques which substantially increase the humidity level in the enclosed space. Asbestos may be removed from pipes, ceilings, etc. by a high pressure water spray to reduce the level of airborne asbestos fibers or friable count compared to many "dry" removal techniques. Asbestos may also be encapsulated rather than removed by spraying a sealant over the asbestos containing material, as explained more fully below. Due to these temperature and humidity conditions, asbestos abatement operators frequently work in the enclosed space for relatively short time periods. As an example, an operator may don his protective clothing and respirator in a special clean changing area, enter the enclosed asbestos removal area, perform removal, cleanup or sealing operations for 20 or 30 minutes, return to a dirty changing area to remove his protective clothing, enter an adjoining shower area to rinse off any asbestos particles, continue to the clean changing area, rest outside the enclosed area for 15 minutes, then repeat the process.
The above described procedure substantially reduces the operator's productivity due to the long time required for operator preparation, cleanup, and rest. A great deal of expense is also incurred in the purchase and proper disposal of the operator's protective equipment, since the equipment is typically discarded after each use. Moreover, the operator's productivity within the work area is relatively poor, even though he is working at his peak output, due to the combination of the protective equipment and the adverse temperature and/or high humidity environment. The rest time required for the operator due to high fatigue when working within the enclosed place is thus only part of the reason for the overall poor productivity and high cost for the asbestos abatement operator. As a result of his poor working environment, frustrated asbestos abatement operations have been known to disregard proper safety procedures, e.g., by removing or short circuiting respiratory equipment to increase their productivity within the enclosed space. This practice not only violates governmental regulations, but more importantly subjects the worker, and indirectly his employer, to substantial safety risks and litigation.
Some asbestos abatement procedures do not require the removal of all the asbestos, but rather may seal or encapsulate some of the remaining asbestos in place with a liquid sealant. After the majority of the asbestos has been removed from a working space, preferably using a wet removal technique to maintain a low friable count of fibers, a "skin layer" of remaining asbestos or asbestos remaining in thin cracks or crevices may be sealed in place using a "lock down" procedure. Typically three or more coatings of sealant or "lock down" must be sprayed on the remaining asbestos containing material, and each coating must cure prior to applying the next coat. The high humidity within the enclosed space results in long curing times, and operators typically return each day to apply a new coat over the coating sprayed the previous day. This long curing time results in increased personnel and equipment costs, which again substantially increases the overall cost of this procedure.
Although the above described problems have long been known in the asbestos abatement industry, no practical solution has heretofore solved these problems. As a result, the productivity of asbestos abatement workers remains very low, and the cost of providing and disposing of protective equipment is high. Building owners are justifiably concerned about asbestos contamination, but are also concerned about asbestos abatement procedures which may contaminate areas in buildings which previously did not contain asbestos. Abatement contractors and building owners are also justifiably concerned about safety shortcuts and litigation.
A related problem concerns the removal or abatement of hazardous particulate material from outdoor structures and components. While the working space within a building is typically partially formed by creating a temporary wall or barrier, the entire working zone may be defined by such temporary barriers while removing asbestos, for example, from outdoor pipes supported on conventional pipe racks. Successive lengths of the pipe lines may be enclosed with plastic sheeting and negative pressure maintained while conducting the asbestos abatement operation, although the adverse temperature and uncontrolled humidity within this working space again lead to low worker productivity and high curing times for lock down operations.
A growing problem concerns the working environment when removing lead-based paint from either indoor or outdoor structures. Lead-based paint can be removed from bridges, tanks, petrochemical towers, and similar structures using blasting operations. The working environment for the blasting operators may be enclosed with a temporary barrier to reduce the contamination of adjoining areas. While this contamination may be at least substantially eliminated by creating a slight negative pressure within the temporary enclosed working space, the elevated temperature and high humidity within the enclosed space, when coupled with the burden of individualised protective equipment and low air flow, inherently creates low worker productivity and the tendency for the blasting operators to avoid proper safety procedures or equipment.
The disadvantages of the prior art are overcome by the present invention, and improved techniques are hereinafter disclosed for removing airborne particulate from a workplace area while increasing the worker's comfort level and thus the productivity of the asbestos abatement personnel.